Apparatus for coding and decoding a digital video signal having duplicate pictures and frames with fields originating from different film source frames

Abstract

A method for coding an input video signal to provide a coded signal. The input video signal has a field rate of 60 Hz and is derived from a motion picture film source using 2-3 pulldown. In the method, first frames, consisting of fields derived from different frames of the motion picture film source, are detected in the input video signal. Then, the input video signal is predictively coded to provide the coded signal by using second frames as reference pictures. Second frames are frames of the input video signal other than the first frames detected in the detecting step. In an alternative method for coding an input video signal to provide a coded signal, duplicate pictures are detected in the input video signal, and duplicate pictures are eliminated from the input video signal to provide an encoder input signal. The encoder input signal is predictively coded using plural predictive coding methods to provide the coded signal. Finally, a skip-picture flag is included in the coded signal in lieu of each eliminated duplicate picture, and a reference picture code identifying a field to be copied to provide each eliminated duplicate picture is also included in the coded signal.

We claim: 
     
       1. A method for coding an input video signal to provide a coded signal, the input video signal having a field rate of 60 Hz and being derived from a motion picture film source using 2-3 pulldown, the method comprising the steps of: detecting in the input video signal first frames consisting of fields derived from different frames of the motion picture film source; and   predictive coding the input video signal to provide the coded signal by using second frames as reference pictures, second frames being frames of the input video signal other than the first frames detected in the detecting step,   wherein the detecting step includes a determining step to determine duplicate fields in the video input signal; and   wherein the predictive coding step includes eliminating the duplicate fields from the input video signal in response to the determining step.   
     
     
       2. The method of claim 1, additionally comprising the steps of: including in the coded signal: a skip-picture flag in lieu of each eliminated duplicate field, and   a reference picture code identifying a field to be copied to provide each eliminated duplicated field.     
     
     
       3. The method of claim 1, wherein, in the predictive coding step, each first frame is coded using bidirectional predictive coding. 
     
     
       4. The method of claim 1, wherein, in the predictive coding step, each first frame is coded using field-by-field mode coding. 
     
     
       5. The method of claim 1, wherein: in the predictive coding step, field-by-field mode coding is applied to each first frame; and   the predictive coding step includes the step of orthogonally transforming each first frame field-by-field.   
     
     
       6. The method of claim 1, wherein: in the predictive coding step, frame-mode coding is applied to each second frame; and   the predictive coding step comprises the step of orthogonally transforming each second frame as a frame.   
     
     
       7. The method of claim 1, wherein, in the predictive coding step, each first frame is coded using field-by-field mode coding and each second frame is coded using frame mode coding. 
     
     
       8. The method of claim 1, additionally comprises the steps of: providing a recording medium;   deriving a recording signal from the coded signal; and   recording the recording signal on the recording medium.   
     
     
       9. A method for coding an input video signal to provide a coded signal, the method comprising the steps of: detecting duplicate pictures in the input video signal, wherein the detecting step includes a determining step to determine duplicate fields in the video input signal,   eliminating each duplicate picture from the video signal to provide an encoder input signal in response to the determining step;   predictive coding the encoder input signal using plural predictive coding methods to provide the coded signal;   including in the coded signal: a skip-picture flag in lieu of each eliminated duplicate picture; and   a reference picture code identifying a field to be copied to provide each eliminated duplicate picture.     
     
     
       10. The method of claim 9, wherein, in the step of detecting duplicate pictures, a picture in the input video signal exhibiting one of little and no change relative to another picture in the input video signal is detected. 
     
     
       11. A system for deriving a recording signal from an input video signal and for reproducing the recorded signal to provide an output video signal, the recording signal having a bit rate substantially lower than the input video signal and the output video signal, the input video signal and the output video signal having a field rate of 60 Hz, the input video signal being derived from a motion picture film source using 2-3 pulldown, the system comprising: an encoding apparatus, comprising: detecting means for detecting in the input video signal first frames consisting of fields derived from different frames of the motion picture film source,   predictive coding means for predictively coding the video input signal to provide the recording signal, the predictive coding means coding each first frame using field mode coding and coding each second frame using frame mode coding, a second frame being a frame of the input video signal other than a first frame detected by the detecting means, and   means for including in the recording signal a processing mode flag indicating a coding mode for each frame of the input video signal; and     a decoding apparatus, comprising: extracting means for extracting the processing mode flag for each frame from the recording signal; and   means for applying inverse predictive coding to the recording signal to provide the output video signal, the inverse predictive coding for each frame having the coding mode indicated by the processing mode flag extracted by the extracting means wherein:       in the encoding apparatus: the detecting means is for detecting duplicate fields in the input video signal, and   the encoding apparatus additionally comprises:   means responsive to the determining means for eliminating the duplicate fields from the input video signal; and   means for including in the recording signal: a skip-picture flag in lieu of each eliminated duplicate field, and   a reference picture code identifying a field to be copied to provide each eliminated duplicated field; and in the decoding apparatus:         the extracting means is additionally for extracting the skip-picture flag and the reference picture code from the recording signal; and   the means for applying inverse prediction coding is additionally for copying, in response to the skip picture flag, the field indicated by the reference picture code to restore an eliminated duplicate field to the output video signal.   
     
     
       12. A system for deriving a recording signal from an input video signal and for reproducing the recorded signal to provide an output video signal, the recording signal having a bit rate substantially lower than the input video signal and the output video signal, the system comprising: an encoding apparatus, comprising: detecting means for detecting duplicate pictures in the input video signal;   means responsive to the detecting means for eliminating each duplicate picture from the input video signal to provide an encoder input signal;   predictive coding means for predictively coding the encoder input signal using plural predictive coding methods to provide the recording signal; and   means for including in the recording signal: a skip-picture flag in lieu of each eliminated duplicate picture, and   a reference picture code identifying a field to be copied to provide each eliminated duplicate picture; and       an decoding apparatus, comprising: means for extracting the skip picture flag and the reference picture code from the recording signal;   means for applying inverse predictive coding to the recording signal to provide the output video signal; and   means for copying, in response to the skip picture flag, the picture indicated by the reference picture code to restore an eliminated duplicate field to the output video signal.